P473: DEVELOPMENT OF POTENTIAL BIOMARKERS FOR IRAK4 INHIBITOR EMAVUSERTIB IN HUMAN ACUTE MYELOID LEUKEMIA
Authors: A. Ugolkov, M. Pilichowska, C.-C. Li, R. C. Hok, M. Samson, M. Lane, R. Von Roemeling, R. Martell
Journal: HemaSphere (2022)

Background: Acute myeloid leukemia (AML), the second most common form of leukemia in adults, remains a highly fatal disease. Interleukin-1 receptor-associated kinase 4 (IRAK4) has been demonstrated as a potential therapeutic target in human AML. IRAK4-mediated activation of NF-kappaB signaling pathway could play a critical role in NF-kappaB-regulated survival and chemoresistance of cancer cells. The results of ongoing Phase 1 study demonstrated clinical activity of IRAK4 inhibitor emavusertib (CA-4948) in patients with relapsed/refractory AML and high-risk MDS. To support the development of companion diagnostic for emavusertib, we developed an immunohistochemical (IHC) assay and explored expression of potential biomarkers in bone marrow (BM) samples obtained from AML patients. Aims: The objective of the present study was to analyze expression of IRAK4, NF-kappaB p-p50 and NF-kappaB p-p65 by IHC staining in human AML with further evaluation of these molecules as potential biomarkers for emavusertib therapy in AML patients. Methods: We used IHC staining and immunoblotting to determine the expression of IRAK4, NF-kappaB p-p50 S337 and NF-kappaB p-p65 S536 proteins in human leukemia cell lines and clinical AML samples. Exploratory biomarker evaluations were performed using serial sections of formalin-fixed paraffin-embedded BM clot samples obtained from 19 AML patients. Eight BM AML samples were purchased from Analytical Biological Services and 11 BM samples were obtained at the screening from evaluable patients with relapsed/refractory AML enrolled in CA-4948-102 clinical trial. Results: Using IHC staining, we found IRAK4 nuclear expression in blasts in 9/19 AML cases. To the best of our knowledge, this is the first report showing nuclear accumulation of IRAK4 in cancer cells. In support of our findings in clinical AML samples, we detected IRAK4 protein expression in nuclear lysates prepared from leukemia cell lines THP-1, HL-60 and K562. Using AML BM samples, we found that IRAK4 nuclear expression in blasts was significantly correlated with activation of NF-kappaB as determined by nuclear accumulation of NF-kappaB p-p50 and p-p65 in 9/19 cases. Cytoplasmic expression of IRAK4 was detected in 2/19 cases whereas IRAK4, NF-kappaB p-p50 and p-p65 expression was not detectable in 8/19 cases of AML. Clinical response data will be presented in the context of these novel findings. Summary/Conclusion: Our findings uncovered a previously unknown nuclear expression of IRAK4 in leukemia cells. Our results demonstrated co-expression of nuclear IRAK4, NF-kappaB p-p50 and p-p65 in blasts suggesting a potential novel mode of interaction between IRAK4 and NF-kappaB in human AML. Although the role of nuclear IRAK4 in leukemia cells remains to be investigated, our preliminary findings revealed new perspectives into emavusertib treatment stratification and demonstrate the possibility of discovering novel biomarkers through IHC analysis of clinical samples. Additional accrual is ongoing to better define emavusertib biomarkers in AML patients.